CFCs (chlorofluorocarbons) and HCFCs (hydrochlorofluorocarbons), which have been conventionally used as refrigerants for refrigeration equipment, have become objects of regulations due to the problem of recent ozone layer depletion, and HFCs (hydrofluorocarbons) are used as refrigerants instead of them.
In the case where a CFC or HCFC is as a refrigerant, hydrocarbon oils such as mineral oil and alkylbenzenes have been used suitably as a refrigerating machine oil. However, depending the type of the coexistent refrigerant, the refrigerating machine oil may exhibit unpredictable behavior, such as compatibility with the refrigerant, lubricity, solution viscosity with the refrigerant, and thermal and chemical stability, and therefore the refrigerating machine oil needs to be developed for each refrigerant. Thus, as refrigerating machine oils for an HFC refrigerant, for example, polyalkylene glycol (see Patent Literature 1), ester (see Patent Literature 2), carbonic acid ester (see Patent Literature 3), and polyvinyl ether (see Patent Literature 4) have been developed.